1. Field of the Invention
This invention pertains to apparatus for calculating and displaying the amount of the sale of gasoline dispensed from a pump and, more particularly, to such apparatus including electronic computation and liquid crystal display.
2. Description of the Prior Art
The economic need for increasing efficiency in all aspects of petroleum production, refining, transportation and distribution has become more intense with the increasing cost of petroleum and ever-increasing labor cost.
In the retailing of gasoline, the computation of the amount of gallonage and the sale price of gasoline dispensed is still made mechanically through gear wheels in most gasoline pumps. Moreover, the display of the result of the computations is also made through read-out wheels. Although devices and methods have been developed for calculating electronically the amount and price of gasoline dispensed through the pump, the replacement of the entire pump is extremely expensive. The development of better display of the gallonage dispensed and the sale price has been hindered by the requirement for intrinsic safety and the lack of background lighting in the totally enclosed dispensing apparatus, such as an electric pump.
Most mechanical apparatus still in use in gasoline pumps often does not have the capacity to compute and display the total price at present prices per gallon. Many gasoline pumps now in use have read-out wheels with a maximum capacity of $9.99. There is not room in this present apparatus for the mechanical expansion of counting and read-out wheels to increase this maximum capacity.
A difficulty of at least equal importance arises from the fact that the increasing price of gasoline has the effect of driving the mechanical computation devices and the read-out wheels at much higher rates than was intended in their construction. For this reason, the mechanical parts, even of new units, are wearing out very rapidly with the necessity of replacing parts with outmoded elements.
Yet another problem with high count rates is that a scrambling of data has been found to occur as the mechanical computing apparatus runs at speeds above that originally intended, and wear factors affect the precision of the mechanical computations. What often results is that the dollar read-outs on opposite sides of the pump will differ.
With the increased rate of turning of the read-out wheels, it is increasingly probable that the maximum purchase price given by the customer will be overrun. It is therefore desirable to have read-out devices that clearly and accurately reflect the sale as it is developing. This is particularly true in self-service equipment where nonexperienced customers are dispensing the gasoline and simultaneously trying to read the dials.
With the increasing cost of gasoline, it is foreseeable that the price will reach and exceed $1.00/gallon. Most present gasoline pumps have a maximum price capacity/gallon of 99.9 cents. Provisions must be made quickly to provide gasoline pumps which will dispense gasoline if the price reaches $1.00/gallon.
The provision of electronic computing and display ability in conjunction with a gasoline pump is complicated by the requirement of intrinsic safety in electrical circuits and equipment in the dispensing of gasoline. The standard for intrinsically safe electrical circuits and equipment for use in hazardous locations (UL 913) applies to the dispensing of gasoline. As such, the standard provides that any conceivable short or malfunction which could cause an arc to occur may not have enough available energy to ignite a stoichiometric mixture of gasoline and air. This intrinsic safety greatly limits the interrelated voltage and amperage of electrical circuits and elements which may be used in gasoline pumps. (See, for example, FIG. 15.1 of Part II of Standard UL 913-Underwriters' Laboratories.)
Liquid crystal display panels have very low voltage operation and very low power dissipation, but do not themselves emit light. Such panels have in the past been thought to have no utility for sale display of gasoline-dispensing apparatus because it was thought that artificial light would have to be supplied behind them, i.e., from an area subject to the intrinsically safe standards. In addition, the light emitted from a liquid crystal display panel has been polarized and is visible only from directly in front of the panel. As such, the panel could not be used for general viewing purposes.
There is, therefore, a pressing need for a modern sale computing and display package which can be fitted into gasoline-dispensing apparatus currently in use with minimum modification and expense, while complying with the intrinsically safe requirements.